[issue42315] `python -m` semantics conflict with `__file__`'s being optional

[Brett Cannon]

Change by Brett Cannon :


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nosy:  -brett.cannon

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[issue42315] `python -m` semantics conflict with `__file__`'s being optional

[William Schwartz]

New submission from William Schwartz :

`python -m mod` sets `sys.argv[0]` to the `mod.__file__` according to 
https://docs.python.org/3.9/using/cmdline.html#cmdoption-m

> If ["-m"] is given, the first element of sys.argv will be the full path to 
> the module file (while the module file is being located, the first element 
> will be set to "-m").

But `__file__` may not exist according to 
https://docs.python.org/3.9/reference/import.html#__file__

> __file__ is optional. If set, this attribute’s value must be a string. The 
> import system may opt to leave __file__ unset if it has no semantic meaning 
> (e.g. a module loaded from a database).

More technically, `__spec__.origin` is the source of `__file__`, and the former 
may be `None`, according to 
https://docs.python.org/3.9/library/importlib.html#importlib.machinery.ModuleSpec.origin

> (__file__)
>
> Name of the place from which the module is loaded, e.g. “builtin” for 
> built-in modules and the filename for modules loaded from source. Normally 
> “origin” should be set, but it may be None (the default) which indicates it 
> is unspecified (e.g. for namespace packages).

`python -m mod` sets sys.argv[0] to `mod.__spec__.origin` at 
3.9/Lib/runpy.py:196

It seems clear to me that the code is doing the right thing relative to the 
documentation for `-m`. But as #26388 and 
https://github.com/indygreg/PyOxidizer/issues/307 show, embedded Python runs 
into the semantic conflict with the documented behavior of `__spec__.origin` 
and `__file__`.


My proposed resolution of this contradiction is to set `sys.argv[0] = 
sys.orig_argv[0]` or, even better, `sys.argv[0] = sys.executable` when 
`PyConfig.run_module` is set but the named module's `__spec__.origin` is `None`.

--
components: Interpreter Core, Library (Lib)
messages: 380689
nosy: William.Schwartz, brett.cannon, eric.snow, ncoghlan
priority: normal
severity: normal
status: open
title: `python -m` semantics conflict with `__file__`'s being optional
type: behavior
versions: Python 3.10, Python 3.8, Python 3.9

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